Fixation of topically applied fluoride in enamel

Effect of a fluoridated etching gel on enamel morphology and shear bond strength of orthodontic brackets

The purpose of this study was to compare the enamel morphology and shear bond strengths of orthodontic brackets bonded to enamel etched with a fluoridated or a nonfluoridated phosphoric acid gel. Ten extracted third molars were used for the enamel morphology evaluation. The buccal surfaces were divided in two sections separated by an occlusogingival groove. One side was etched for 60 seconds with a 38% phosphoric acid gel, and the other side was etched with a 60% phosphoric acid gel containing 0.5% sodium fluoride. The specimens were then examined with a scanning electron microscope. For the shear bond strength tests, 30 extracted third molars were used. The buccal enamel surfaces of the mesial cusp were used, and the teeth were randomly divided into two groups of 15 teeth each--group 1, 38% phosphoric acid gel for 60 seconds; group 2, 60% phosphoric acid gel with 0.5% sodium fluoride for 60 seconds. Orthodontic lingual buttons were bonded to the etched surfaces with a composite resin. The results showed that the overall morphologic etching effect was similar in both groups. The mean shear bond strength for group 1 was 11.8 MPa +/- 4.2, and for group 2 it was 16.5 MPa +/- 5.1. This difference was statistically significant (p less than 0.01).

Physical and chemical considerations of the role of firmly and loosely bound fluoride in caries prevention

Historically, there has been considerable debate concerning the roles of loosely bound (calcium fluoride) and firmly bound (fluorapatite) fluoride for caries prevention. Research now shows that fluorapatite (FAP) is a finite reaction product of enamel/apatite fluoridation with or without CaF2 formation, suggesting that CaF2 always be considered as a supplement to, rather than a substitute for, FAP formation. In the presence of low levels of fluoride in the solution phase, the crystallization of hydroxyapatite is enhanced, while the corresponding dissolution is retarded. Fluoride in the bulk FAP or CaF2 solid phase, in contrast, has limited impact on crystal growth or dissolution kinetics. Both FAP and CaF2 can provide F to the solution phase to enhance remineralization and retard demineralization of enamel HAP crystallites. The FAP provides most of this F under low pH conditions, while CaF2 provides F at neutral or lower pH. The reactivity of fluoride on sound and carious enamel differs significantly. Carious enamel acquires more fluoride, acquires it more quickly, and itself acts as a source of retained fluoride in comparison with the more limited reactivity of sound enamel. Overall, the most important question concerning fluoride reactivity relates to its efficiency in enhancing remineralization or retarding demineralization processes. This is influenced not only by the reaction products, e.g., loosely or firmly bound fluoride, but also by the nature of the enamel substrate and frequency of application of the topical fluoridating agent. Inasmuch as the reactivity of bulk HAP is dominated by surface layers of FAP material, the debate over usefulness of various fluoride reaction products solely on a chemical level is no longer critical. Instead, all factors influencing the efficiency of a fluoridating regimen must be considered in the development of improved systems for caries prevention.

On the role of calcium fluoride in the cariostatic mechanism of fluoride

The literature concerning the formation and stability of CaF2 in the oral environment is reviewed. In early work the CaF2 formed during topical application with fluoride was assumed to be beneficial. It was suggested that it could protect the enamel surface directly or provide free fluoride ions for subsequent incorporation into the hydroxyapatite lattice. However, McCann claimed, in 1968, that CaF2 is soluble in saliva (12-15 mg/l), that it would be rapidly lost in the oral cavity, and that the clinical effect of fluoride was related to formation of firmly bound fluoride only. In this period many authors reported total loss of CaF2 during 24 h after a topical application of fluoride. It has now been shown in several laboratories that calcium fluoride is stable in saliva at neutral pH owing to surface adsorption of HPO2-4 to the crystal surface and formation of a solubility-limiting phase. Extended exposure of saliva can cause formation of a fluorapatite layer on the CaF2 crystals, restricting their dissolution further. Low pH (pH less than 5) causes loss of the solubility-limiting adsorbed HPO2-4 and a slow dissolution of CaF2. The CaF2 crystals may thus serve as pH-controlled reservoirs of fluoride ions on the enamel or in plaque and release fluoride during caries challenges. It is suggested that calcium fluoride is an essential phase explaining important aspects of the mechanism of topically applied fluoride, contrary to what was assumed in the past.

The effect of fluoride in phosphoric acid on enamel fluoride uptake and the tensile bond strength of an orthodontic bonding resin

Decalcification that occurs adjacent to bonded orthodontic brackets is of great concern to orthodontists. Among the many procedures suggested to overcome this problem is the addition of fluoride to the phosphoric acid (H3PO4) etching solution. The purposes of this study were to determine the loss of fluoride from the acidic etching solutions, to evaluate the effect of various fluoride concentrations in H3PO4 on the tensile bond strength of an orthodontic bonding resin, to determine the amount of total and bound fluoride acquired by etched enamel, and to evaluate the effect of these etching solutions on enamel by scanning electron microscopy. Solutions of 50 m/m% H3PO4 containing 0 and approximately 0.01, 0.04, 0.08, 0.2, 0.4 and 0.9% fluoride were prepared. The fluoride concentrations in the etching solutions remained stable up to 3 months after preparation. The tensile bond strengths of the bonding resin to the etched enamel surfaces were not significantly different. Enamel acquired the greatest amount of total fluoride from H3PO4 solutions containing 0.215% fluoride while the bound fluoride acquired by enamel from the fluoride-containing etching solutions was not significantly different. The addition of fluoride to H3PO4 did not impede the etching effect on enamel.

Effect of fluoride-containing alginates and gels on the acid resistance of demineralized human enamel

A series of in vitro studies were carried out to determine the effect of commerically available alginate impression materials and gels on enamel solubility. This was performed by 4-min topical application of the tested products on partially demineralized enamel surfaces. The difference in the amounts of calcium and phosphorus dissolved in acetate buffer before and after topical treatment was considered a measure of the reduction in enamel solubility. All topically applied materials except APF-gel (Gelution) exerted a considerable reduction in enamel solubility ranging between 41.4% and 61.5% in 0.2 M acetate buffer. Successive enamel solubility tests in weak acetate buffer (0.01 M) showed that Gelution was inferior to the other tested products. No simple relationship exists between the fluoride content of these products and their antisolubility effect.

The effect of a NaF solution and a fluoride varnish on the acid resistance of root dentin

Sectioned root dentin surfaces were treated with either a NaF solution for 10 min or a fluoride varnish for 48 h and then exposed to 1 M acetate buffer pH 5.8 for 20 h. Microradiographs of non-fluoride treated specimens (controls) regularly showed a partially demineralized zone extending from the surface. The NaF-treated specimens exhibited a lesion with alternating radiopaque and radiolucent zones, which had a mean total depth equal to that of the controls. The varnish-treated specimens showed a demineralized zone which was significantly less deep than those observed in the two other groups. Elemental analyses performed by an electron microprobe showed a positive correlation between the amount of F incorporated and the acid resistance of the tissue.

The effect of contact time of acidulated phosphate fluoride on fluoride concentration in human enamel

Polished enamel blocks with known surface areas were obtained from human mandibular incisors. Acidulated phosphate fluoride was applied for 4 min and washed off after additional contact times of 0, 2, 6 and 24 h, respectively. The enamel fluoride concentrations were determined in three successive etch depths before and after extraction in 1 M KOH for 24 h. The predominant reaction product was CaF2. The concentration of the fluoride bound as fluorapatite or fluorhydroxyapatite reached an optimal level after a 6-h contact time.

A 2-year report on caries prevention by fluoride varnishes in a community with fluoridated water

The benefit of semi-annual applications of sodium fluoride varnish (Duraphat) and silane fluoride varnish (Fluor Protector) was studied in 11-13 year-old children with life-long exposure to fluoridated drinking water (1-1.2 parts/10(6)). Annual clinical and radiographic examinations were made on 67 children in the Duraphat group and 71 children in the Fluor Protector group. Fluoride varnish was applied semi-annually using the half-mouth technique. At the end of 2 years, the mean overall DMFS-increments on the control side and test side of the Duraphat group were 5.0 and 3.8 (p less than 0.01), respectively, and of the Fluor Protector group 3.7 and 3.3 (NS). The caries reductions were 24% and 12%, respectively. Since there were no differences between initial mean DMFS scores of the groups, it was assumed that lower increments in the Fluor Protector group were due to Fluoride ions crossing the midline and providing protection on the control side as well. When increments in the Duraphat control side and the Fluor Protector test side were compared, the caries reduction of Fluor Protector was 35% (p less than 0.01). Fluoride varnishes provide additional benefit even when fluoride intake from drinking water is optimal.

The effect of topical fluorides, after acid etching of enamel, on the bond strength of directly bonded orthodontic brackets

This study tests the hypothesis that the beneficial effects of topical fluoride can be realized without reducing the bond strength of the resin adhesive. Twenty-eight groups of four teeth (third molars and premolars) were extracted from twenty-eight patients and stored in distilled water. Twin brackets on Ormesh pads were bonded to all teeth with Endur adhesive. One tooth from each group was bonded according to the manufacturer's instructions. These teeth, Subgroup I, served as controls. Subgroup II teeth were etched for 4 minutes with 50% phosphoric acid containing 2 percent sodium fluoride. Subgroup III teeth received a 3-minute application of a basic phosphate fluoride solution (10(-2)M NA3PO4, 10(3) ppm F) after 1 minute of etching with 50 percent phosphoric acid. Subgroup IV teeth received a 4-minute application of 8 percent stannous fluoride solution after 1 minute of etching with 50 percent phosphoric acid. Each tooth was mounted in a block of improved dental stone; guide wires were used to reproduce bracket orientation. The M.T.S. materials-testing apparatus was used to generate a torsional moment on the bracket at a rate of 1 degree per second. Fluoride uptake by enamel has been shown to be greater in an acid medium or after acid etching. The application of directly bonded orthodontic brackets and pit-and-fissure sealants requires acid etching of the enamel surface. This study supports the use of topical fluoride after acid etching, a procedure that achieves the benefits of increased fluoride uptake without changing the bond strength of the resin adhesive.

Effect of fluoride topical solutions on enamel demineralization by lactate buffers and Streptococcus mutans in vitro

Applications of APF and NaF solutions to extracted human teeth reduced the extent of enamel subsurface demineralization induced by colonization of S. mutans but were ineffective against demineralization by acid lactate buffers. It is concluded that the CaF2 formed on the tooth surface during the treatment is responsible for the protection observed.

Antiplaque potential of topical stannous fluoride

Sterile enamel samples treated by topical application of 10% stannous fluoride were incubated with S mutans and S sanguis respectively and with a mixed culture to which L casei had been added. The results were compared with sterile nonfluoridated enamel samples subjected to the same procedures. The parameters compared were postincubation pH values, bacterial concentrations on the surfaces, and enamel surface alterations. Stannous fluoride treated samples consistently yielded higher pH readings than nonfluoridated samples; the concentration of microorganisms adhering to the surfaces was conspicuously reduced on the pretreated enamel when compared by scanning electron microscopy to untreated samples, as were enamel surface alterations. These findings lend support to other recent investigations which have shown that fluorides act in several ways to inhibit cariogenesis in addition to reducing hydroxyapatite solubility.

Kinetic calcium, phosphate, and fluoride dissolution after topical fluoride application to intact enamel surfaces

In a system without accumulation of products dissolved from enamel, the total mineral dissolved was reduced by about 10% for NaF- and SnF2-treated surfaces and was increased by about 10% for APF-treated surfaces. Accumulation in solution of products dissolved from the enamel surfaces enhanced surface remineralization to account for a net decreased dissolution as compared with dissolution without accumulation of products.

Assessment of the reliability of radiographic diagnosis in a clinical caries trial

A method of repeated assessment of radiographic study material was used in an attempt to develop indices of consistency and reliability. The interpretation of the coefficient of reliability was complicated by the large intersubject variability relative to examiner error. Of the various indices generated, the F tests for replications and for treatment by replication interaction are suggested as useful immediately.

Effects of various topical fluorides on subsequent mineralization and dissolution of enamel

Acid-etched surfaces of enamel were given topical applications of neutral NaF, acid NaF, APF, and SnF2 solutions (about 1% F in each). After a four hour delay following topical application, the surfaces were mineralized in a calcium phosphate solution and then subjected to acid dissolution. Fluoride released from the enamel surfaces was measured during mineralization and subsequent acid dissolution. Results of both processes, and the fluoride released during both processes, indicate that a neutral NaF gave the best results.

Sealing of developmental pits and fissures. IV. Measurement of in vivo fluoride pickup by electron microprobe x-ray spectrophotometry

Analysis with an electron microprobe X-ray spectrophotometer revealed that high levels of fluoride were retained in enamel 30 or more days after in vivo application of a fluoride-releasing polyurethane adhesive coating to human teeth. Analyses of calcium and phosphorus concentrations also indicate that remineralization occurred after application of the polyurethane, despite preliminary acid etching.

Sealing of developmental pits and fissures. II. Fluoride release from flexible fissure sealers

A fluoride-releasing polyurethane adhesive coating was found to be effective in reducing the acid solubility of enamel in vitro and the incidence of carious lesions of rat molars in vivo; this indicates that the coating would be an efficient topical fluoride system for application to developmental pits and fissures and all other surfaces of teeth.

Demineralization studies of fluoride-treated enamel using scanning electron microscopy

Enamel was treated with topical stannous fluoride and demineralized with an acetate buffer for varying periods. A scanning electron microscope comparison of the surface alterations revealed that stannous fluoride inhibited surface alterations when challenged by the acid. Evidence suggested that fluoride plays a role in the remineralization of repair of slightly etched enamel surfaces.

A study of inorganic constituents in dental plaque

The presence of human enamel did not affect the inorganic composition of plaque grown under standardized conditions on an intraoral device. Only enamel recently topically treated with fluoride increased plaque-fluoride concentrations beyond the average value of 25 ppm dry weight (about a tenth of previously reported values).

Release of fluoride into saliva after topical fluoride application

Fluoride uptake by the surface enamel of teeth treated with fluoride solutions in vitro and fluoride release into saliva after topical applications in vivo were determined. The fluoride uptake after NaF + Na2HPO4 treatment was higher than that after NaF treatment. The fluoride release into saliva was less after NaF + Na2HPO4 than after NaF application, pointing to a greater permanent fluoride fixation.